1. Field of the Invention
The present invention is generally in the field of electrical circuits. More particularly, the invention is in the field of line drivers.
2. Background Art
Line drivers, such as voltage mode and current mode line drivers, are typically utilized to drive transmission lines in cell phones, set top boxes, cable modems, DSL modems, and other types of electronic devices. To prevent return loss and signal distortion, a line driver is typically required to provide an output impedance that matches the characteristic impedance of the transmission line. For example, a line driver in a video application is required to provide a 75 Ohm output impedance to drive a 75 Ohm load via 75 Ohm video cables. Although current mode line drivers can provide a desirable performance, they typically have higher power consumption than voltage mode line drivers. As a result, voltage mode line drivers are typically utilized in devices in which power is limited, such as mobile communications devices.
In a conventional implementation, a voltage mode line driver includes a voltage amplifier coupled in series with a termination resistor, which is coupled to a load resistor via a transmission line. To prevent impedance mismatch, the termination resistor should have the same value as the load resistor and the characteristic impedance of the transmission line. However, as a result of the voltage divider formed by the termination resistor and the load resistor, the output voltage provided by the voltage amplifier needs to be twice as large as the output voltage provided at the line driver output, which requires a high power supply voltage. The high power supply voltage required by this conventional voltage mode line driver undesirably increases power consumption.